Tetra-substituted methanes as organic photoconductors

ABSTRACT

Certain bis(N,N-dialkylaminoaryl)dialkylmethanes and gem-bis(N, N-dialkylaminoaryl)cycloalkanes are useful as photoconductors in electrophotographic elements.

Norman Geaflrey Rule RMIheMer, N11. 062,960

01:1. 26, 19711 Emmmmn 1101111111 Company fiknchmfier, 1931/.

Inventor Appl. No. Filed Patented Aasignee TETMA-SMESTHTIUTIED ME'IIHANIES AS ORGANIC IPIHIOTOCUNDKJCTUMRS 13 Cflmilms, N6 Drawings 003 s/os 11 112161 011 Search 96/1, 1.5, 1.6; 260/571, 576

[56] mefferelnces Ci1ed UNITED STATES PATENTS 2,034,491 3/1936 Sloan 260/576 2,505,470 4/1950 Green 260/5 76 2,536,640 l/l951 Hayten 260/576 3,140,948 7/1964 Stewart 96/48 3,232,755 2/1966 Hoegl et a1. 96/1 3,274,000 10/1966 Noe et a1. 96/1 3,310,401 3/1967 Greig 96/1.5 3,317,315 5/1967 Nicoll et al. 96/1.1

Primary Examiner-George F. Lesmes Assistant Examiner-John C. Cooper Att0rneys-William H. J. Kline, James R. Frederick and Fred L. Denson ABSTRACT: Certain bis(N,N-dia1k.y1aminoaryl)dialkylmethanes and gem-bis(N,N-dialkylaminoaryl)cycloalkanes are useful as photoconductors in electrophotographic elements.

This invention relates to electrophotography, and in particular to photoconductive compositions and elements.

The process of xerography, as disclosed by Carlson in US. Pat. No. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material whose electrical resistance varies with the amount of incident electromagnetic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. it is then exposed to pattern of actinic radiation which has the effect of differentially reducing the potential of this surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible 2 by contacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or discharge pattern as desired. Deposited marking material can then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor, or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic charge pattern can be transferred to a second element and developed there.

Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. For example, vapors of selenium and vapors of selenium alloys deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in the present-day document-copying applications.

Since the introduction of electrophotography, a great many organic compounds have also been screened for their photoconductive properties. As a result, a very large number of organic compounds have been known to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions.

Typical of these organic photoconductors are the triphenylamines and the triarylmethane leuco bases. Optically clear photoconductor-containing elements having desirable electrophotographic properties can be especially useful in electrophotography. Such electrophotographic elements can be exposed through a transparent base if desired, thereby providing unusual flexibility in equipment design. Such compositions, when coated as a film or layer on a suitable support, also yield an element which is reusable; that is, it can be used to form subsequent images after residual toner from prior images has been removed by transfer and/or cleaning. Thus far, the selection of various compounds for incorporation into photoconductive compositions to form electrophotographic layers has proceeded on a compound-by-compound basis. Nothing as yet has been discovered from the large number of different photoconductive substances tested which permits effective prediction, and therefore selection of the particular compounds exhibiting the desired electrophotographic properties.

it is, therefore, an object ofthis invention to provide a novel class of photoconductors having high photosensitivity when electrically charged.

it is another object to provide novel photoconductor-containing compositions which exhibit high electrical speeds.

it is a further object of the invention to provide an improved process utilizing the novel photoconductors described herein.

Also, it is yet another object of this invention to provide electrophotographic elements containing the novel photoconductors described herein.

These and other objects of the invention are accomplished by employing certain tetra-substituted methane derivatives as photoconductors. Useful methane derivatives include:

a bis(N,N-dialkylaminoaryl)dialkylmethanes and 5 b gem-bis(N,N-dialkylaminoaryl)cycloalkanes.

The aryl moiety in the above-described compounds can be further substituted by various groups including alkoxy having one to eight carbon atoms such as methoxy, ethoxy, propoxy, butoxy, etc., hydroxy, halogen such as chlorine, bromine, etc.

The alkyl groups of these compounds generally contain one to 18 carbon atoms and include substituted alkyl groups. Also, the cycloallcanes include bicycloalkanes and can contain from four to 20 carbon atoms. The nuclei of the cycloalkanes can be further substituted by other subs'tituents such as those 15 described in the following paragraphs.

A large number of substituted diarylmethanes and triarylmethanes have exhibited photoconductive properties when used as photoconductors in electrophotographic elements. Typical of these are the leuco base of malachite green, bis(4- dimethylaminophenyl)phenylmethane and bis(4- dimethylaminophenyl)-methane as described in British Pat. Nos. 984,965 and 980,879. Also, diarylmethane compounds have been used as activators for zinc oxide photoconductors. Such uses are described in British Pat. No. 1,141,666. According to this invention, it has been found that the photoconductors described herein have enhanced speed and/or stability over those photoconductors described. in the prior art. Also, from an economic standpoint, the materials described herein 3 are substantially less expensive than other related compounds used for the same purpose. in particular, substantial increases in speed are obtained compared to speeds attainable with many other closely related compounds which do not have the central methyl carbon atom substituted by the groups set forth above. These increases in speed are observed when the photoconductor is incorporated into a coating composition, coated onto a support and the coating accepts a suitable potential (e.g. 500-600 volts). The relative speed of the coating is determined on the basis of the reciprocal of the exposure required to reduce the potential of the: surface charge to 100 volts (toe speed). The term toe speed" is known in the photographic art with reference to H and D" curves. As used herein, the term refers to corresponding curves resulting from exposure plotted against voltage. The reduction of the surface potential to 100 volts or below is significant in that it represents a requirement for suitable broad area development of an electrostatic image. The relative speed at 100 volts is a measure of the ability to produce and hence to develop or otherwise utilize the electrostatic latent image. When many conventional photoconductors are used, the surface potential frequently does not drop to or below 100 volts and therefore no speed can be assigned to such a composition. When most photoconductors are used in photoconductive compositions, the surface potentials of such resultant compositions usually drop below 100 volts, and thus, a definite speed can be ascertained. However, these speeds are improved when the photoconductors of this invention are employed. The preferred tetra-substituted methane derivatives useful as photoconductors in the present invention are characterized by the following formula:

Ra Ra R1\ 1'11 R3 /N 4 1- rr .32. A .BL

7 wherein:

R,, R R and R.,are each lower aliphatic alkyl groups having one to 18 carbon atoms such as a methyl group, a propyl group, an ethyl group, a pentyl group, a hexyl group, an isobutyl group, a 3-methypentyl group, an octyl group,

etc.;

R and R each represent any of the following groups:

1. a lower aliphatic alkyl having one to 18 carbon atoms, typically including those set forth above for R R R and R 2. a lower alkoxy having one to l8 carbon atoms, e.g.,

methoxy, ethoxy, propoxy, butoxy, etc.;

3. hydrogen; or

4. halogen such as chlorine, bromine, fluorine, or iodine;

R and R can be the same or different substituents, each representing any of the following;

1. an aliphatic alkyl group having one to 18 carbon atoms e.g., methyl, ethyl, propyl, butyl, isobutyl, octyl, dodecyl, etc. including a substituted alkyl group having one to 18 carbon atoms such as a. alkoxyalkyl e.g., ethoxypropyl,

propoxymethyl, etc., b. aryloxyalkyl e.g., phenoxyethyl, naphthoxymethyl,

phenoxypentyl, etc., c. aminoalkyl e.g.,

aminopropyl, etc.,

d. hydroxyalkyl e.g., hydroxypropyl, hydroxyoctyl,

hydroxymethyl, etc.,

e. aralkyl e.g., benzyl, phenethyl, etc.,

methoxybutyl,

aminobutyl, aminoethyl,

f. alklaminoalkyl e.g., methylaminopropyl,

methylaminoethyl, etc., and also including dialkylaminoalkyl e.g., diethylaminoethyl,

e.g., cyanopropyl, cyanobutyl,

wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naphthyl, etc., lower alkyl having one to eight carbon atoms e.g., methyl, ethyl, propyl, etc., amino including substituted amino e.g., diloweralkylamino, lower alkoxy having one to eight carbon atoms e.g., butoxy, methoxy, etc., aryloxy e.g., phenoxy, naphthoxy, etc.;

2. a cycloalkyl group having four to eight carbon atoms in the cyclic nucleus e.g., cyclobutyl, cyclohexyl, cyclopentyl, etc. including a substituted cycloalkyl group such as a. alkoxycycloalkyl e.g., ethoxycyclohexyl, methoxycyclobutyl, propoxycyclohexyl, etc.,

b. aryloxycycloalkyl, e.g., phenoxycyclohexyl,

naphthoxycyclohexyl, phenoxycyclopentyl, etc.,

c. aminocycloalkyl, e.g., aminocyclobutyl, aminocyclohexyl, aminocyclopentyl, etc.,

d. hydroxycycloalkyl e.g., hydroxycyclohexyl, hydroxycyclopentyl, hydroxycyclobutyl, etc.,

e. arylcycloalkyl e.g., phenylcyclohexyl,

cyclobutyl, etc.,

f. alkylaminocycloalkyl e.g., methylaminocyclohexyl,

methylaminocyclopentyl, etc. and also including dialkylaminocycloalkyl e.g., diethylaminocyclohexyl, dimethylaminocyclobutyl, dipropylaminocyclooctyl, etc.,

g. arylaminocycloalkyl, e.g., phenylaminocyclohexyl,

diphenylaminocyclohexyl, N-phenyl-N-ethylaminocyclopentyl, N-phenyl-N-methylaminocyclohexyl, naphthylaminocyclopentyl, etc.,

h. nitrocycloalkyl, e.g., nitrocyclobutyl, nitrocyclohexyl, nitrocyclopentyl, etc.,

phenyli. cyanocycloalkyl, e. g. cyanocyclohexyl, cyanocyclobutyl, cyanocyclopentyl, etc., j. halocycloalkyl e.g., chlorocyclohexyl, bromocyclopentyl, chlorocyclooctyl, etc., k. cycloalkyl substituted with an acyl group having the formula wherein R is hydroxy, hydrogen, aryl e.g., phenyl, naphthyl,

etc., amino including substituted amino e.g., diloweralkylamino, loweralkoxy having one to eight carbon atoms e.g.,

butoxy, methoxy, etc., aryloxy, e.g., phenoxy, naphthoxy, etc.,

lower alkyl having one to eight carbon atoms e.g., methyl, ethyl, propyl, butyl, etc.,

3. when taken together comprise the atoms necessary to complete a cycloalkylidene group having four to 20 carbon atoms in the cyclic nucleus including a bridged cycloalkylidene group, e.g., cyclobutylidene, cyclopentylidene, cyclohexylidene, cycloheptylidene, norcarylidene, norpinylidene, norbornylidene including a substituted cycloalkylidene group having four to 20 carbon atoms such as a. alkoxycycloalkylidene e.g., ethoxycyclohexylidene,

methoxycyclobutylidene, propoxycyclohexylidene, methoxynorbornylidene, etc.,

b. aryloxycycloalkylidene, e.g., phenoxycyclohexylidene, napthoxycyclohexylidene, phenoxycyclopentylidene, phenoxynorcarylidene, etc.,

o. aminocycloalkylidene, e.g., aminocyclobutylidene, aminocyclohexylidene, aminocyclopentylidene, aminonorpinylidene, etc.,

d. hydroxycycloalkylidene, e.g., hydroxycyclohexylidene, hydroxycyclopentylidene, hydroxycyclobutylidene, hydroxynorbornylidene, etc.,

. alkylcycloalkylidene, e.g., dimethylcycloalkylidene, cyclohexylcycloalkylidene 4-(1, l, 3', 3'- tetramethylbutyl)cyclohexlidene, etc.,

f. arylcycloalkylidene, e.g., phenylcyclohexylidene,

phenylcyclobutylidene, phenynorcarylidene, etc.,

g. alkylaminocycloalkylidene, e.g., methylaminocyclohexylidene, methylaminocyclopentylidene, etc., and also including dialkylaminocycloalkylidene, e.g., diethylaminocyclohexylidene, dimethylaminocyclobutylidene, dipropylaminocyclooctylidene, diethylaminonorpinylidene, etc.,

h. arylaminocycloalkylidene, e.g., phenylaminocyclohexylidene, diphenylaminocyclohexylidene, N- phenyl-N-ethylaminocyclopentylidene, N-phenyl-N- methylaminocyclohexylidene, naphthylaminocyclopentylidene, phenylaminonorbornylidene, etc.,

i. nitrocycloalkylidene, e.g., nitrocyclobutylidene, nitrocyclohexylidene, nitrocyclopentylidence, etc.,

j. cyanocycloalkylidene, e.g., cyanocyclohexylidene,

cyanocyclobutylidene, cyanocyclopentylidene, etc.,

k. halocycloalkylidene, e.g., chlorocyclohexylidene, bromocyclopentylidene, chlorocyclooctylidene, etc.,

. cycloalkylidene substituted with an acyl group having the formula JLR wherein R is hydroxy, hydrogen, aryl e.g., phenyl, napthyl, etc., amino including substituted amino e.g., diloweralkylamino, loweralkoxy having one to eight carbon atoms e.g., butoxy, methoxy, etc., aryloxy e.g., phenoxy, naphthoxy, etc., lower alkyl having one to eight carbon atoms e.g., methyl, ethyl, propyl, butyl, etc.

Typical compounds which belong to the herein-described general class of photoconductive materials include the following compounds listed in Table I below:

Table l l 2,2-bis(4-hl,N-dimethylaminophenyl)propane ll 2,2-bis(l -N,hl-diethylaminophenyl)propane ill l,l-bis(d-ll,N-dimethylarninophenyl )cyclohexane lV bis(2,2bis(d -hl,N-diethylarninophenyl)butane V 2,2-bis(4-hl,l l-diethylaminophenyl)heptane Vi l,3,3-tris( iN,l-l-diethylaminophenyl)butane Vil l,l-bis(l-N,N-diethylaminophenyl)cyclohexane Vlll l,l-bis(4--l,N-di-n-propylaminophenyl)cyclohexane lX l,l-bis( l-hhethyl N-methylaminophenyl)cyclohexane X l,l-bis( i-hl,N-diethylaminophenyl)-4-methylcyclohexane Xi i,l-bis( lhl,hl-diethylaminophenyl)-3-methylcyclohexane Kill l, l -bis( bbi,l l-diethylaminopheny)-4-( l methylpropyU- cyclohexane I illil i,l-bis( l-hl,hl-diethylaminophenyl)-4-( l ',1',3',3,- tetramethyibutyl)cyclohexane MW 1, i -bis( 4-N,N-diethylaminophenyl)-3,4-dimethylcycloheirane Xi/ l,l-bis(4-hl,Il-diethylaminophenyl)3,5-dimethylcycloxhexane Will 2l4, l-bis( l-N,N-diethylaminophenyl)cyclohexyl]-2- cyciohexylpropane ill/ll i,l-bis( l-i l,N-diethylaminophenyl)cyclopentane XVlll l,l-bis(4-l-l,N-diethylaminophenyl)cycloheptane XIX 2,2'bis( lNN-diethylaminophenyl)norbornane Xl'i h hd',4-tetrakis(4-N,bl-diethylaminophenyl)bicyclohexane ZOtl 2,2-bis[ l, i-bis(p-ll,N-diethylaminophenyl)cyclohexyllpropane Kllll 2-( l,- l-{bis( l-hl,N-diethylaminophenyl)cyclohexyl])-2- (4-1 il-N,hl-diethylaminophenyl]cyclohex-3-enyl)propane )tXlll 2,2-bis( l-hLN-diethylamino-2chlorophenyl)propane )UtlV 2,2-bis( l-N,N-diethylamino-Z-methoxy)propane lElectrophotographic elements of the invention can be prepared with the photoconducting compounds of the invention in the usual manner, i.e., by blending a dispersion or solution of a photoconductive compound together with a binder, when necessary or desirable, and coating or forming a selfsupporting layer with the photoconductor-containing material. Mixtures of the photoconductors described herein can be employed. Likewise, other photoconductors known in the art such as those described in Light Belgian Pat. No. 705,117 dated Apr. 16, 1968 can be combined with the present photoconductors. in addition, supplemental materials useful for changing the spectral sensitivity or electrophotosensitivity of the element can be added to the composition of the element when it is desirable to produce the characteristic effect of such materials.

The photoconductive layers of the invention can also be sensitized by the addition of effective amounts of sensitizing compounds to exhibit improved electrophotosensitivity. Sensitizing compounds useful with the photoconductive compounds of the present invention can be selected from a wide variety of materials, including such materials as pyrylium dye salts including thiapyrylium dye salts and selenapyrylium dye salts disclosed in Van/illan et al. U.S. Pat. No. 3,250,615; fluorenes, such as 7,12-dioxo-l3-dibcnzo(a,h)fluorene, 5,10- dioxoia,l l-diazobeno(b)fluorene, 3,l3-dioxo-7-oxadibenzo(b,g)fluorenes, and the like; aggregate-type sensitizers of the type -oxadibenzo(b,g)fluorene, in Belgian Pat. No. 705,! 17 dated Apr. 16, 1968; aromatic nitro compounds of the kinds described in U.S. Pat. No 2,610,120; anthrones like those disclosed in U.S. Pat. No. 2,670,284; quinones, U.S. Pat. No. 2,670,286; benzophenones U.S. Pat. No. 2,670,287; thiazoles U.S. l st. No. 2,732,30l; mineral acids; carboxylic acids, such maleic acid, dichloroacetic acid, trichloroacetic acid and salicyclic acid; sulfonic and phosphoric acids; and various dyes, such as cyaninc (including carbocyanine), mero cyanine, diarylrnethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, aze, anthraquinone dyes and the like and mixtures thereof. The sensitizers preferred for use with the compounds of this invention are selected from pyrylium salts including selenapyrylium salts and thiapyrylium salts, and cyanine dyes including carbocyanine dyes. Where a sensitizing compound is employed with the binder and organic photoconductor to form a sensitized electrophotographic element, it is the normal practice to mix a suitable amount of the sensitizing compound with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed in the coated element. Other methods of incorporating the sensitizer or the effect of the sensitizer may, however, be employed consistent with the practice of this invention. In preparing the photoconductive layers, no sensitizing com pound is required to give photoconductivity in the layers which contain the photoconducting substances, therefore, no sensitizer is required in a particular photoconductive layer. However, since relatively minor amounts of sensitizing com pound give substantial improvement in speed in such layers, the sensitizer is preferred. The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.000] to about 30 percent by weight based on the weight of the film forming coating composition. Normally, a sensitizer is added to the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.

Preferred binders for use in preparing the present photoconductive layers are film-forming, hydrophobic polymeric binders having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicon resins; styrene-alkyd resins; silicone-alkyd resins; soyaalkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methyl methacrylate), poly(n-butyl methacrylate), poly(isobutyl methacrylate), etc., polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly[ethylene-co-alkylenebis(alkyleneoxyaryl)phenylenedicarboxylate1; (alkyleneoxyaryl) phenolformaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly[ethylene-co-isopropylidene-2,2-bis(ethyleneoxyphenylene)terephthalate]; copolymers of vinyl haloarylates and vinyl acetate such as poly(vinyl m-bromobenzoate-co-vinyl acetate); etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trade names as Vitel PE-lOl, Cymac, Piccopale l00, Saran lF-220, lLexan I05 and Lexan 145. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.

Solvents useful for preparing coating compositions with the photoconductors of the present invention can include a wide variety of organic solvents for the components of the coating composition. For example, benzene; toluene; acetone; 2-butanone, chlorinated hydrocarbons such as methylene chloride; ethylene chloride; and the like; ethers, such as tetrahydrofuran and the like, or mixtures of such solvents can advantageously be employed in the practice of this invention.

in preparing the coating compositions utilizing the photoconducting compounds disclosed herein useful results are obtained where the photoconductive substance is present in an amount equal to at least about 1 weight percent of the coating composition. The upper limit in the amount of photoconductive material present can be widely varied in accordance with usual practice. it is normally required that the photoconductive material be present in an amount ranging from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductive material in the coating composition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a wet coating thickness in the range of about 0.001 inch to about 0.01 inch is useful in the practice of the invention. A preferred range of coating thickness is from about 0.002 inch to about 0.006 inch before drying although such thickness can vary widely depending on the particular application desired for the electrophotographic element.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of the electrically conducting supports, for example, various conducting papers; aluminum-paper laminates; metal foils, such as aluminum foil, zinc foil, etc., metal plates, such as aluminum, copper, zinc, brass, and galvanized plates; vapor-deposited metal layers such as silver, nickel or aluminum on conventional film supports such as cellulose acetate, poly(ethylene terephthalate polystyrene and the like conducting supports.

An especially useful conducting support can be prepared by coating a transparent film support material such as poly(ethylene terephthalate) with a layer containing a semiconductor dispersed in a resin. A suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of a maleic anhydride-vinyl acetate copolymer, cuprous iodide and the like. Such conducting layers and methods for their optimum preparation and use are disclosed in U.S. Pat. Nos. 3,007,901, 3,245,833 and 3,267,807.

The compositions of the present invention can be employed in photoconductive elements useful in any of the well known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element held in the dark, is given a blanket positive or negative electrostatic charge as desired by placing it under a corona discharge to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as for example, by a contact-printing technique, or by lens projection of an image, or reflex or bireflex techniques and the like, to thereby form an electrostatic charge image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the fact that light energy striking the photoconductor causes the electrostatic charge in the lightstruck areas to be conducted away from the surface in proportion to the illuminance on a particular area.

The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charged or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive particles having optical density. The developing electrostatically responsive particles can be in the form of a dust, or powder and generally comprise a pigment in a resinous carrier called a toner. A preferred method of applying such a toner to an electrostatic charge image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following U.S. Pat. Nos: 2,786,439; 2,786,440; 2,786,441; 2,811,465; 2,874,063; 2,984,163; 3,040,704; 3,117,884 and reissue Re 25,779. Liquid development of the electrostatic charge image may also be used. In liquid development the developing particles are carried to the image-bearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, U.S. Pat. No. 2,297,691 and Australian Pat. No. 212,315. In dry developing processes the most widely used method of obtaining a permanent record is achieved by selecting a developing particle which has as one of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the charge image or powder image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after developing and fusing or fusing respectively. Techniques of the type indicated are well known in the art and have been described in a number of U.S. and foreign patents, such as U.S. Pats. Nos. 2,297,691 and 2,551,582, and in RCA Review, vol. 15 (1954) pages 469-484.

The compositions of the present invention can be used in electrophotographic elements having many structural varia tions. For example, the photoconductive composition can be coated in the form of single layers or multiple layers on a suitable opaque or transparent conducting support. Likewise, the layers can be contiguous or spaced having layers of insulating material or other photoconductive material between layers or overcoated or interposed between the photoconductive layer or sensitizing layer and the conducting layer. It is also possible to adjust the position of the support and the conducting layer by placing a photoconductor layer over a support and coating the exposed face of the support or the exposed or overcoated face of the photoconductor with a conducting layer. Configurations differing from those contained in the examples can be useful or even preferred for the same or different application for the electrophotographic element.

The following examples are included for a further understanding of this invention.

Example I The following composition is sheared in a Waring Blender for 30 minutes at room temperature:

Binder-Lexan I45 [trade name of General Electric Company for a poly (4,4'- isopropylidenedi henylcne carbonaleH 1.0 g. Sensitizer [2,6-diphenyl-4-(4- dimethylaminophcnyl)lhiu yrylium erchlorate] 0.025 g. Dichluromethane 9.6 g.

A photoconductor (0.25 g.) is then dissolved in the resultant heterogeneous mixture which is then coated at 0.004 -inch wet thickness on a poly(ethylene terephthalate) support which has been precoated with an evaporated nickel conducting layer. The element is then dried at F. The electrophotographic element is charged under a negative corona sourceuntil the surface potential, as measured by an electrometer probe, reaches about 600 volts. It is then subjected to exposure from behind a stepped-density gray scale to a 3000 K. tungsten source. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V to some lower potential, V, whose exact value depends on the actual amount of exposure in meter-candle-seconds received by the area. The results of the measurements are plotted on a graph of surface potential V vs. log exposure for each step. The top speed is the numerical expression of 10multiplied by the reciprocal of the exposure in meter-candle-seconds required to reduce the 600 -volt charged surface potential to volts. The speeds of several elements prepared in this manner using various photoconductors are listed in Table ll below:

V 1,050 Vll 900 Vlll 800 IX 1,000 )(Vll 1,000 XV"! Example ll Example 11 is repeated except the sensitizer is replaced by 2,6-bis-(4-ethylphenyl)-4-(amyloxyphenyl)thiapyrylium perchlorate. lllelatively good speeds are obtained. Similarly good results are obtained when 2,4bis-(4 ethyl-phenyl)-6-(4- styrylstyryl)pyrylium perchlorate is used. Example ill in order to demonstrate the increase in speed attainable using the instant photoconductors, example 1 is repeated using a photoconductor of the type described in British Pat. Nos. 980,879 and 984,964. The photoconductor employed is bis(N,N-dimethylaminophenylmethane). The speed obtained is 500 which is substantially lower than the speeds obtained using the photoconductors of this invention.

Example lV Another comparison is made using 1,l-bis(4-N,N- diethyIarnino-Z-methylphenyl)-l-phenylmethane as the photoconductor. The speed is determined in the same manner as example l and is found to be 458. Example V Coating dopes are prepared in the manner described in example 1 using the materials set forth therein. The photoconductors employed are compounds l-XXlV in Table I. [n a darkened room, the surface ofeach of the photoconductive layers so prepared is charged to a potential of about +600 volts under a corona charger. The layer is then covered with a transparent sheet bearing a pattern of opaque and light-transmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about 75 metercandles for 12 seconds. The resulting electrostatic charge image is developed in the usual manner by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles on glass beads functioning as carriers for the toner particles. A good reproduction of the pattern results in each instance. Similar results are obtained using a liquid developer.

The photoconducting compounds of this invention can generally be prepared by synthesis familiar to those skilled in the art. Typical preparations are set forth in the following examples.

Example Vi 2,2 bis(4-N,N-diethylaminophenyl)propane (11) A mixture of acetone (29.0 g), concentrated hydrochloric acid (100 ml.) and N,Ndiethylaniline (150 g.) is heated to reflux. it is then made alkaline and steam-distilled to remove unreacted N,N-diethylaniline. The organic residue is extracted into benzene, dried (CaCland isolated by evaporating the solvent. The crystalline residue is recrystallized from ethanol to give l.2 g. ofproduct, m.p. 84.1-84.9.

Analysis. Calculated for C H N C, 81.7; H, 10.1; N, 8.28. Found: C, 81.6; H, 10.1;N, 8.3.

Example Vll l,1-bis(4-N,N dimethylaminophenyl)cyclohexane (111) The product prepared by the condensation of cyclohex anone and N,N-dimethylaniline in concentrated hydrochloric acid as described by J. V. Braun et. al. Ann. 472, 29 (1929) after purification by column chromatography and recrystallization from cyclohexane has a m.p. 156.0-157.0.

Analysis. Calculated for C H N C, 82.1; H, 9.22; N, 8.70. Found: C, 82.7; H, 8.8; N, 8.7.

Example Vlll 2,2-bis(4-N,N-diethylaminophenyl)butane (IV) A mixture of 2-butanone (36g) N,N-diethylaniline (149g), concentrated hydrochloric acid (70 ml.) and ethanol (12.5 ml.) is placed in sealed pressure bottles which are heated in a steam bath. The flask contents are steam distilled, made a1- kaline with solid sodium hydroxide and again steam distilled. The organic residue is extracted into benzene, dried (MgSO evaporated down and distilled to give 28.0 g. of product, b.p. 160202 (0.2 mm.).

Analysis. Calculated for C H N C, 81.7; H, 10.3; N, 7.97. Found: C, 81.8; H, 9.8; N, 8.1.

Example lX 2,2-bis(4-N,Ndiethylaminophenyl)heptane (V) A mixture of Z-heptanone (114.2 g), N,N'diethylaniline (300 g.), concentrated hydrochloric acid ml.) and ethanol (25 ml.) is refluxed. It is then made alkaline and steam distilled. The residual organic material is extracted into benzene, washed with brine, dried (MgSO.,) and concentrated under reduced pressure. The residue is distilled, and the fraction with hp. 180-233.5 (0.3 mm.) on standing deposits crystals. This fraction is triturated twice with cold methanol and the resultant solid is crystallized three times by chilling solutions made up in tepid methanol-ethyl ether to give 16.7 g. of product, m.p. 42.0-44.0.

Analysis. Calculated for C H N C, 82.18; H, 10.73; N, 7.10.

Found: C, 81.9; H, 10.7; N, 7.3.

Example X l,3,3,-tris(4-diethylaminophenyl)butane (V1) A mixture of 4-hydroxy-2-butanone (132 g.) N,N- diethylaniline (450 g.), concentrated hydrochloric acid ml.) and ethanol (20 ml.) is refluxed. It is then steam distilled, made neutral with sodium hydroxide and again steam distilled. The organic residue is taken up in ethyl ether, dried Na,co, and concentrated by evaporation of the solvent. The residue is distilled to remove the fraction boiling below l50/1.3 mm. Hg. The distillation residue is taken up in hot ethanol, and the solid which precipitates on cooling the solution is recrystallized twice from nitromethane to give 20 g. of product, m.p. 76-77.

Analysis. Calculated for C H N C, 81.7; H, 9.8; N, 8.4. Found: C, 81.5; H, 9.9; N, 8.6.

Example X1 l,l-bis(4-N,N-diethylaminophenyl)cyclohexane (V11) A mixture of cyclohexanone (98.0 g.), N,N-diethylaniline (298 g.), concentrated hydrochloric acid (92 ml.) and ethanol (25 ml.) is heated to reflux. The reaction mixture is made alkaline and the organic layer which separates is extracted into benzene. The benzene solution is washed with water, dried (MgSO evaporated down, diluted with methanol and al lowed to stand. The solid which separates out is recrystallized from methanol-ethyl acetate to give 93.0 g. of product, m.p. 89.5-90.5.

Analysis. Calculated for C H N C, 82.49; H, 10.12; N, 7.40. Found: C, 82.7, 82.4;1-1. 10.3, 9.9; N, 7.6,7.6.

Example Xll l,1-bis(4-N,N-di-n-propylaminophenyl)cyclohexane (V111) A mixture of N,N-di-n-propylaniline (177.3 g.), cyclohexanone (49.0 g.) concentrated hydrochloric acid (70 ml.) and ethanol (10 ml.) is refluxed. It is then made alkaline and the organic phase is extracted into benzene, washed with brine, dried (MgSO and concentrated by evaporation of the benzene. The residue is distilled to give 119.5 g. of product, b.p. 245 (0.2 mm. Hg).

Analysis. Calculated for C ,,H N C, 82.8; H, 10.65; N, 6.45. Found: C, 82.6;1-1, 10.5; N, 6.7.

Example Xlll 1,l-bis(4-N-ethyl-N-methylaminophenyl)cyclohexane (1X) A mixture of cyclohexanone, (98.0 g.), N-ethyl-N- methylaniline (270 g.), concentrated hydrochloric acid (140 ml.) and ethanol (25 ml.) is refluxed and then is made alkaline and steam distilled. The organic residue readily crystallizes and is washed with water and recrystallized from ethanol benzene to give 109.7 g. of product, m.p. l22.5-123.4. Analysis. Calculated for C H N C, 82.25; H, 9.78; N, 7.99. Found: C, 82.4; H, 9.8; N, 8.3.

Example XIV 1,1-bis(4-N,N-diethylaminophenyl)-4methy1cyclohexane (X) A mixture of 4-methylcyclohexanone (112.0 g.) N,N- diethylaniline (300 g.) and concentrated hydrochloric acid (110 ml.) is refluxed. It is then made neutral with sodium hydroxide and steam distilled. The organic residue is extracted with benzene, dried (Na Co and concentrated by evaporation of the solvent. The solid residue is recrystallized from nitromethane to give 75 g. of colorless crystalline product, m.p. 105-106.

Analysis. Calculated for C21HwN2: C, 82.6; H, 10.2; N, 7.13. Found: C, 82.7; H, 10.3; N, 6.9.

Example XV l ,1-bis(4-N,N-diethylaminophenyl)-3-methylcyclohexane A mixture of 3-methylcyclohexanone (100 g.), N,N- diethylaniline (266 g.), concentrated hydrochloric acid (125 ml.), and ethanol (25 ml.) is refluxed. 1t is then made alkaline and steam distilled. The organic residue is extracted into benzene, washed with brine, dried (MgSO,) and concentrated under vacuum. The residue solidifies when cooled and triturated with methanol. The solid is recrystallized from methanol-ethyl acetate to give 88 g. of product, m.p. 83.6"- 85.l.

Analysis. Calculated for C H N z C, 82.6; H, 10.3; N, 7.16. Found: C, 83.0; H, 10.3; N, 7.0.

Example XVl l,1-bis(4-N,N-diethylaminophenyl)4-(1'-methylpropyl)cyclohexane (Xll) A mixture of 4-( l '-methylpropyl)cyclohexanone (123.5 g.) N,N-diethylaniline (239 g.), concentrated hydrochloric acid (100 ml.) ethanol (25 ml.) is refluxed and then is made alkaline and steam distilled. The organic residue, which solidifies on standing, is washed with water and recrystallized from ethanol-ethyl acetate to give 136.7 g. of product, m.p. 95.3- 97.0.

Analysis. Calculated for C H N z C, 83.50; H, 10.7; N, 6.45. Found: C, 82.8; H, 10.7; N, 6.6.

Example XVII 1,1-bis(4-N,N-diethylaminophenyl)-4-( l',l ',3,3- tetramethylbutyl)cyclohexane (X111) A mixture of 4-(1',1,3,3-tetramethy1bulyl) cyclohexanone (105 g.), N,N-diethylaniline (149 g.), concentrated hydrois then made alkaline and steam distilled. The organic residue is extracted into benzene, washed with brine, dried (MgSO and concentrated by evaporation of the solvent. A small portion of the residue is distilled and a fraction b.p. 217-268 (0.3 mm.) gives crystalline solid on trituration with ethanol. The main bulk of the residue, on similar trituration and seeding, also gives a solid which gives 17.5 g. of product, m.p. 91.l-93.0.

Analysis. Calculated for C H N C, 83,1; H, 11.1 N, 5.7. Found: C, 82.8; H, 10.7; N, 6.4.

Example XVlll 1 l-bis(4-N,N-diethylaminopheny1)-3,4-dimethylcyclohexane (XlV) A mixture of 3,4-dimethylcyclohexanone (170 g.), N,N- diethylaniline (400 g.), concentrated hydrochloric acid (135 ml.) and ethanol (20 ml.) is refluxed. It is then steam distilled, made neutral with sodium hydroxide and again steam distilled. The organic residue is extracted into toluene, dried (Na Co and concentrated by evaporation of the solvent. The residue is distilled and the fraction with hp 215 (0.12 mm. Hg.) is recrystallized from ethanol to give 55 g. of product, m.p. 92-93.

Analysis. Calculated for C, H N,. C, 82.8; H,10.3;N,6.89. Found.C,82.9;H, 10.7; N,7.l.

Example XIX 1,1-bis( 4-N,N-diethylaminophenyl)-3,S-dimethylcyclohexane A mixture of 3,S-dimethylcyclohexanone (100 g.), N,N,- diethylaniline (240 g.), concentrated hydrochloric acid (80 ml.) and ethanol (10 ml.) is refluxed. It is then steam distilled to remove excess ketone, neutralized and again steam distilled to remove excess N,N-diethylaniline. The organic residue is extracted into ethyl ether, dried (Na,CO,) and concentrated by evaporation of the solvent. The residue is distilled to give a fraction, b.p. 225 (0.12 mm.), which when taken up in hot ethanol and cooled yields 10 g. of crystalline product, m.p. 89-90.

Analysis. Calculated for C, H ,N,: C, 82.8; H, 10.3; N, 6.89. Found: C, 82.7; H, 10.6; N, 7.1.

Example XX 2[4,4-bis(4-N,N-diethylaminophenyl)cyclohexyl]-2-cyclohexylpropane (XVl) A mixture of 4-( 2-cyclohexylisopropyl)cyclohexanone 1 1 l g.), N,N-diethylaniline (149 g.), concentrated hydrochloric acid (50 ml.) and ethanol (10 ml.) is refluxed. It is then steam distilled to remove unreacted ketone, made neutral with sodium hydroxide and again steam distilled to remove unreacted N,N-diethylaniline. The organic residue is extracted with ethyl ether, dried (N a CO;,) and concentrated by evaporation of the solvent. The residue is dissolved in cyclohexane and filtered through a bed of neutral alumina. The alumina is eluted with several further portions of cyclohexane. The combined filtrates are evaporated down and the solid residue is recrystallized from ethanol to give 50 g. of product, m.p. 1 10-1 1 1. Analysis. Calculated for C H N,: C, 83.7; H, 10.7; N, 5,58. Found: C, 83.4; H, 10.7; N, 5.8.

Example XXl l,1-bis(4-N,N-diethylaminophenyl)cyclopentane (XVII) A mixture of cyclopentanone (168 g.), N,N-diethylaniline (600 g.), concentrated hydrochloric acid (200 ml.) and ethanol (10 ml.) is refluxed. It is then steam distilled to remove excess ketone, made neutral and again steam distilled to remove excess N,N-diethylaniline. The organic residue is taken up in benzene, dried (Na,CO,) and concentrated by evaporation of the solvent. The residue, which solidifies on standing, is recrystallized from ethanol to give 25 g. of product, m.p. 99100.

Analysis. Calculated for C H N C, 82.4; H, 9.88; N, 7.68. Found: C, 82,0; H, 10.0; N, 7.7.

Example XXII 1,1-bis(4-N,N-diethylaminophenyl)cycloheptane (XVlll) A mixture of cycloheptanone g.), N,N-diethylaniline (266 g concentrated hydrochloric acid (100 ml.) and ethanol (25 ml.) is refluxed. It is then made alkaline and steam distilled. The residue is extracted into benzene, washed, with brine, dried (MgSO and concentrated by evaporation of the solvent. The residue solidifies on being triturated with cold methanol. The solid when recrystallized from methanol-ethyl acetate gives 12.3 g. of product, m.p. 76.0-76.9.

Analysis. Calculated for C ,H N C, 82.60; H, 10.26; N, 7.35.

Found: C, 82.6; H, 10.1; N, 6.9.

Example XXlll 2,2-bis(4-N,N-diethylaminophenylnorbornane (XlX) A mixture of Z-norbornanone (97 g.), N,N,-diethylaniline (300 g.), concentrated hydrochloric acid ml.) and ethanol (25 m1.) is refluxed. It is then made alkaline and steam distilled. The organic residue, which readily solidifies is filtered off, washed with water, and recrystallized from ethanolbenzene to yield 13.5 g. of product, m.p. 120.0-122.0. Analysis. Calculated for C H M: C, 83.0; H, 9.82; N, 7.18. Found: C, 82.8; H, 9.4; N, 7.6.

Example XXIV 4,4,4,4-tetrakis(4-N,N-diethylaminophenyl)bicyclohexane A mixture of 4,4'-bicyclohexanone (49.0 g.), N,N- diethylaniline (240 g.), concentrated hydrochloric acid (100 ml.) and ethanol 10 ml.) is refluxed. It is then made acid with hydrochloric acid and extracted with methylene chloride. The aqueous layer is neutralized with sodium hydroxide. The organic solid which separates is filtered off, dried, and recrystallized from xylene to give 85 g. of product, m.p. 264-265. Analysis. Calculated for C H Nn C, 82.9; H, 9.8; N, 7.42. Found: C, 83.3;H, 9.9; N, 7.6.

Example XXV 2,2-bis[4,4-bis(p-N,N-diethylaminophenyl)cyclohexyl] propane (XXI) A mixture of 2,2-bis(44-oxo-cyclohexyl)propane (43.0 g.), N,N diethylaniline (110 g.), concentrated hydrochloric acid (44 m1.) and ethanol (25 m1.) is refluxed. It is then made alkaline and steam distilled. The aqueous phase is then decanted from the semisolid organic residue which is washed with water, and recrystallized from ethanol benzene to give 18.0 g. of product, which melts at 2 l2l 1.5".

Analysis. Calculated for C l'l Np C, 82.9; H, 10.1; N, 7.05. Found: C, 82,8;11, 10.1; N, 7.1.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Iclaim:

1. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a polymeric film-forming binder, an organic photoconductor and a sensitizer for said organic photoconductor, said sensitizer being present in an amount from about 0.001 to about 30 percent based on the weight of said photoconductive composition, said organic photoconductor having the formula wherein R R R and R each represent an aliphatic alkyl group having one to 18 carbon atoms;

R and R are each selected from the group consisting of hydrogen, an alkyl group, a halogen and an alkoxy group; and R and R are each selected from the group consisting of an aliphatic alkyl group having one to 18 carbon atoms, a cycloalkyl group and, when taken together comprise the atoms necessary to complete a cycloalkylidene group.

2. The electrophotographic element of claim 1 wherein said photoconductor is a bis(N,N-dialkylaminoaryl)dialkylmethane.

3. The electrophotographic element of claim 1 wherein said photoconductor is a bis(N,N-dialkylaminoaryl)cycloalkane.

4. The electrophotographic element of claim 1 wherein R and R are taken together to complete a cycloalkylidene group.

5. The electrophotographic element of claim 1 wherein R and R are taken together to complete a bicycloalkylidene group.

6. The electrophotographic element of claim 5 wherein R,and R are taken together to complete a norbornylidene group.

7. The electrophotographic element of claim 1 wherein R and R are each alkyl groups.

8. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 2,2-bis(4-N,N- dicthylaminophenyl)propane as the organic photoconductor,

b. a filmforming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.

9. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprisin a. from about 18 to about 60 percent by weight based on said photoconductive composition of 2,2-bis(4-N,N- diethylaminophenyl)butane as the organic photoconductor,

b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.

10. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 2,2-bis(4-N,N- diethylaminophenyl)heptane as the organic photoconductor,

b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.

11. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 1,l-bis(4-N-ethyl- N-methylaminophenyl)cyclohexane as the organic photoconductor,

b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.

12. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 1,1-bis(4N,N-

diethylaminophenyl)cyclopentane as the organic photoconductor,

b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.

13. In an electrophotographic process where an electro static charge pattern is formed on an electrophotographic element, the improvement characterized in that said element has a photoconductive layer comprising a tetra-substituted methane photoconductor having the formula wherein R R R and R. each represent an aliphatic alkyl group having one to 18 carbon atoms;

R and R are each selected from the group consisting of hydrogen, an alkyl group, halogen and an alkoxy group; and

R and R are each selected from the group consisting of an aliphatic alkyl group having one to 18 carbon atoms, a cycloalkyl group and, when taken together comprise the atoms necessary to complete a cycloalkylidenc group. 

2. The electrophotographic element of claim 1 wherein said photoconductor is a bis(N,N-dialkylaminoaryl)dialkylmethane.
 3. The electrophotographic element of claim 1 wherein said photoconductor is a bis(N,N-dialkylaminoaryl)cycloalkane.
 4. The electrophotographic element of claim 1 wherein R7 and R8 are taken together to complete a cycloalkylidene group.
 5. The electrophotographic element of claim 1 wherein R7 and R8 are taken together to complete a bicycloalkylidene group.
 6. the electrophotographic element of claim 5 wherein r7and r8are taken together to complete a norbornylidene group.
 7. The electrophotographic element of claim 1 wherein R7 and R8 are each alkyl groups.
 8. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 2,2-bis(4-N,N-diethylaminophenyl)propane as the organic photoconductor, b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.
 9. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 2,2-bis(4-N,N-diethylaminophenyl)butane as the organic photoconductor, b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.
 10. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 2,2-bis(4-N,N-diethylaminophenyl)heptane as the organic photoconductor, b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.
 11. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 1,1-bis(4-N-ethyl-N-methylaminophenyl)cyclohexane as the organic photoconductor, b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.
 12. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a. from about 10 to about 60 percent by weight based on said photoconductive composition of 1,1-bis(4N,N-diethylaminophenyl)cyclopentane as the organic photoconductor, b. a film-forming polymeric binder for said photoconductor and c. 0.005 percent to about 5 percent by weight based on said photoconductive composition of a sensitizer for said photoconductive composition.
 13. In an electrophotographic process where an electrostatic charge pattern is formed on an electrophotographic element, the improvement characterized in that said element has a photoconductive layer comprising a tetra-substituted methane photoconductor having the formula 